The present invention relates to fermentation technology, in particular to the selection of appropriate defoamers and their efficient amounts, for such processes.
The screening and selection of defoamers for the use in fermentation processes is a complex, empirical and time-consuming process. However, in most fermentation processes, the adding of defoamers is critical to the overall yield, due to the fact, that strong foaming fermentation broth is difficult to control and often obliges to lower the filling of the fermenter, hence the overall productivity of each fermentation cycle and batch. Large additions of non appropriated defoamers can also lead to severe troubles in downstream operations like ultrafiltration, microfiltration or ion-exchange processes. Foam is a colloid system of gas dispersed into a liquid. Aeration occurs when dispersed small bubbles are formed in the liquid and remain trapped without coalescing. For the foam formation and stabilisation, a surface-active element is added which is able to form an elastic layer at the surface. Foam is formed when 1) a bubble of gas (in particular air) is developed in a liquid (in particular water) and is immediately coated with the surfactant, 2) the bubble rises to the surface and forms there an elastic skin of surfactant molecules and water, 3) the bubble is stable enough to remain at the surface without breaking. Foam is stabilised by the combined Maragoni and Gibbs effects. They define the surface tension modification, which creates this elastic more or less thick bubble wall. The use of defoamers permits the control of the foam thanks to their specific properties of reducing the surface tension of the bubble, preventing the water and foaming surfactant from entering the bubble, improving their drainage from the bubble and improving the de-aeration.
In most of the fermentation processes, the process requires a strong dispersion of micro-bubbles of air into the media, in order to permit the oxygen transfer from the bubbles towards the micro-organisms. Foam in the fermenter is created, with this high level of aeration, by all components that are present one after the other or together during the process: Nutrients, Biomass, Product, added surfactant, residues etc. Each of these compounds generates a type of foam, which can be different from the other and that cumulate their foaming power. For the best performances, the defoamer should be versatile enough in order to be adapted to each type of foaming components. The performances of the defoamers are characterised in two main properties, the knock-down effect and the hold-out effect. The knock-down effect is the ability of the product to quickly destroy existing foam, whereby the hold-out effect relates to the ability of the product to prevent the foam formation for a long time.
In the past, the selection of appropriate defoamers requires a complete series of laboratory fermentation trials, which are expensive and time consuming. Furthermore, most of the time, the results obtained from the laboratory tests are poorly correlated to the industrial trials.
It is therefore a standing demand in the fermentation industry to develop new test methods which reduce both time and costs for selecting appropriate defoamers for a fermentation processes.